An internal combustion engine for a motor vehicle generally includes an engine block, which defines at least one cylinder accommodating a reciprocating piston, coupled to rotate a crankshaft. The cylinder is closed by a cylinder head that cooperates with the reciprocating piston to define a combustion chamber. A fuel and air mixture is cyclically disposed in the combustion chamber and ignited, thereby generating hot expanding exhaust gasses that cause the reciprocating movements of the piston. The fuel is injected into each cylinder by a respective fuel injector. The fuel is provided at high pressure to each fuel injector from a fuel rail in fluid communication with a high-pressure fuel pump that increases the pressure of the fuel received from a fuel source.
Each of the cylinders has at least two valves that selectively allow air into the combustion chamber from an intake port and alternately allow exhaust gases to exit through an exhaust port. Each of the valves of each cylinder is actuated by a respective cam rotating on camshafts in time with the crankshaft and being connected to the crankshaft by a series of pulleys and a belt or a chain.
Conventional internal combustion engines are also managed by an Electronic Control Unit (ECU) that may receive input signals representative of various physical parameters associated with the engine from various sensors and may execute suitable calculations to determine the relevant physical parameters of each fuel injection.
Among these sensors, a camshaft sensor is provided on one of the camshafts. The sensor is used in combination with a crankshaft sensor to monitor the opening and closing of the valves in relation with the position of the pistons and valves in the engine, especially but not exclusively in engines with variable valve timing.
The camshaft position sensor may be used in combination with a rotating cam target wheel provided with a series of notches on its circumference. The camshaft position sensor may detect a series of notches located on the cam target wheel as they pass in front of the sensor position during rotation of the camshaft. The camshaft sensor may be a Hall effect device or may be based on other detection principles such as an optical sensor or an inductive sensor.
In conventional internal combustion engines, the camshafts have to be installed in a cam carrier by inserting them through bearings provided in seats in the cam carrier while the cam target wheel is machined or already installed on one of the camshafts. In this case, the diameter of the target wheel of the camshaft is limited by the diameter of the bearings, because the camshaft must be moved through the bearings during assembly of the engine. However, a small target wheel diameter leads to a low or to a not optimal accuracy of the cam sensor output signal.
Furthermore, since the camshafts and the crankshaft must be synchronized together, during assembly of the engine, an intermediate locking phase of the camshafts is provided where the camshafts, once inserted into the cam carrier, must be temporarily locked into a fixed position to allow the synchronization with the crankshaft and the pistons of the engine. In order to perform this locking operation, current camshafts have a groove that is machined on their surface and cam carriers are provided with a lateral bore through which the camshaft is locked in place by a special tool that can be inserted into the bore in order to engage the groove.